Contribution of Specific Flour Components to Water Vapor Adsorption Properties of Wheat Flours

The dynamic water vapor adsorption properties were determined for two wheat flours (hard wheat flour and soft wheat flour) and compared with those of flour components (starch, damaged starch, gluten, water-soluble pentosans, and water-insoluble pentosans). Water vapor adsorption rates were determined from the changes in sample mass as a function of time during hydration after a step increase in relative humidity (rh). It was not possible to significantly discriminate the selected products by initial rates of adsorption (5.1 × 10(^-2) to 6.4 × 10(^-2) g/100 g of dry matter/min), except the water-insoluble pentosans that were characterized by high values of adsorption rates (14 × 10(^-2) g/100 g of dry matter/min). Changes in initial relative humidity conditions and %rh step sizes induced significant changes in adsorption rates. Calculations of apparent water diffusion coefficients were done using a derived form of Fick’s law for polydisperse spherical particles. Apparent water diffusion coefficients (at 25(degree)C and 60% rh) were estimated between 2.19 × 10(^-15) and 3.72 × 10(^-15) m(^2)/sec for the selected wheat flours. Water-insoluble pentosans are characterized by the highest values of diffusion coefficients (1.53 × 10(^-13) m(^2)/sec) when compared with the other wheat components. The calculated values of apparent water diffusion coefficient were discussed in regard to experimental conditions.